Front Shifting

Key to the shifting process is the front gear change mechanism called a derailleur or mech. It's a fairly simple process: a cage comprising two guide plates simply pushes the chain one way or the other.

Downshifts, moving to a smaller chainring to make pedaling easier, are delivered by the outer guide plate diverting the chain to the left, so it runs off the teeth of the outer chainring and simply falls onto the teeth of the inner. And upshifts, moving to a larger chainring to make pedaling harder, are achieved by the inner guide plate pressing the chain against the side of the outer chainring, until it catches on the teeth and is carried upwards by them, eventually meshing properly.